Recent economic activities involving mass production, consumption, and disposal have posed global environmental problems such as global warming and resource depletion. In this situation, in order to construct a recycling society, the Home Appliance Recycling Law went into effect in April 2001 that used air conditioners, televisions, refrigerator-freezers, and washing machines must be recycled.
Unneeded home electric appliances have been conventionally crushed at home electric appliance recycling factories and sorted and recovered by material utilizing magnetic force, wind power, vibration, or the like so as to be used as resources. Particularly metal materials are very efficiently recovered as resources using a gravity separator or a magnetic separator; each material such as iron, copper, or aluminum is recovered at a high purity.
On the other hand, for resin materials, polypropylene (PP), which has a low specific gravity, is sorted from materials with high specific gravities by means of gravity separation utilizing water and recovered at a relatively high purity. However, the gravity separation utilizing water very disadvantageously produces a large amount of effluent and fails to sort PS (polystyrene) and ABS (acrylonitrile styrene butadiene), which have similar specific gravities, from each other.
(Patent Document 1) and (Patent Document 2) propose sorting methods taking into account the problems associated with the reuse of resin materials as resources.
The sorting method in (Patent Document 1) utilizes the difference in melting point between two types of resins to be sorted. The sorting method sorts the two types of resins from each other by heating a pair of peripheral moving surfaces made of heat resistant steel so as to have a temperature between the melting temperatures of the two types of resin to be sorted, passing the two types of resins to be sorted from each other through the gap between the heated peripheral moving surfaces to allow only one of the resins having the lower melting temperature to adhere to the heated peripheral surfaces.
Furthermore, the sorting method in (Patent Document 2) utilizes the difference in dielectric loss between resin materials. The sorting method sorts the resin materials from each other by applying an electromagnetic wave or the like to a mixture with at least two types of resins mixed therein to cause dielectric heating and utilizing the difference in melting characteristics between the resin materials based on the difference in heating nature between the resin materials. The above-described sorting methods do not produce effluent or are not affected by the specific gravities of the resin materials.
[Patent Document 1] Japanese Utility Model Laid-Open No. 4-126822
[Patent Document 2] Japanese Patent Laid-Open No. 2002-234031
However, according to (Patent Document 1), in low-polarity molecule substances with low adhesion to other substances such as PP and PS, the melted resin exhibits an unstable adherence strength. This prevents sorting at a high purity. Furthermore, when a resin with a low melting point and a resin with a high melting point pass simultaneously through the gap between the heated peripheral moving surfaces, the unmelted resin with a high melting point adheres to the melted resin with a low melting point, hindering sorting disadvantageously.
Furthermore, (Patent Document 2) fails to sort resin materials exhibiting similar dielectric loss characteristics. This makes recovery at a high purity difficult.
The present invention solves the above-described conventional problems. An object of the present invention is to provide a method of sorting resin materials at a high purity which method prevents the generation of effluent and is not affected by the specific gravity or dielectric loss characteristics of the resin materials.